Polymers which can be fabricated into transparent plastic articles, for example, aromatic polycarbonate resins and blends, are sometimes used in products for the medical field. These products include blood oxygenators, anesthesia canisters, intravenous connectors and accessories, pulsatile balloon pumps, and blood centrifuge banks. Such articles are frequently sterilized, typically by heating in an autoclave, or by contacting with ethylene oxide, or by exposure to ionizing radiation, e.g., gamma radiation or electron beam radiation. Each of these techniques has certain shortcomings, however. Autoclaves are often undesirable because of the thermal instability of many polymers, including polycarbonates and polyarylates, the relatively high energy requirements of the technique, and the residual wetness of the treated article which must first be dried before use.
The utilization of ethylene oxide is often objectionable because of its toxicity, instability and the environmental concerns associated with its disposal.
Sterilization by ionizing radiation is a useful alternative, being an essentially dry process which can be conducted at low temperatures and which is relatively inexpensive. The use of ionizing radiation when applied to articles made of polycarbonate and polyarylate resins in particular usually results, however, in the formation of a yellow coloration in the normally optically clear polymer. This can be regarded as unsightly, and to counteract the effect coloring agents have often been incorporated into the polymer to mask the yellow color which forms with one considered more esthetically acceptable, for instance, a bluish tinge.